"A Nation Once Again" is a song, written in the early to mid-1840s by Thomas Osborne Davis (1814–1845). Davis was a founder of an Irish movement whose aim was the independence of Ireland.

Raymond Daly[1] and Derek Warfield describe Davis's acute awareness that songs could have a strong emotional impact on people. Davis wrote that "a song is worth a thousand harangues". He felt that music could have a particularly strong influence on Irish people at that time. He wrote: "Music is the first faculty of the Irish... we will endeavour to teach the people to sing the songs of their country that they may keep alive in their minds the love of the fatherland."

"A Nation Once Again" was first published in The Nation on 13 July 1844 and quickly became a rallying call for the growing Irish nationalist movement at that time.

The song is a prime example of the "Irish rebel music" subgenre. The song's narrator dreams of a time when Ireland will be, as the title suggests, a free land, with "our fetters rent in twain". The lyrics exhort Irishmen to stand up and fight for their land: "And righteous men must make our land a nation once again".

In 2002, after an orchestrated e-mail campaign,[2][3] the Wolfe Tones' 1972 rendition of "A Nation Once Again" was voted the world's most popular song according to a BBC World Service global poll of listeners, ahead of "Vande Mataram",[4] the national song of India.